Electric condenser and method of making it



Feb. 16, 1932. w. H. PRIESS 1,844,974

ELECTRIC CONDENSER AND METHOD OF MAKING IT Original Filed Aug. 31, 19213 Sheets-Sheet 1 4 Feb. 16, 1932. w. H. PRIESS 1,844,974

ELECTRIC CONDENSER AND METHOD OF MAKING IT Original Filed Aug. 51, 19213 Sheets-Sheet 2 ZZZ Feb. 16, 1932. w. H. PRIESS 1,344,974

ELECTRIC CONDENSER AND METHOD OF MAKING IT Original Filed Aug. 31, 19215 Sheets-Sheet 5 Patented Feb. 16, 1932 UNITED STATES- PATENT OFFICEWILLIAM H. nurse, or NEW YORK, 1mm, Assmnoa, BY MESNE assmnmnurs, TOonu- ERAL mncrmc comm, a oonrona'rron or new YORK ELECTRIC CONbE-NSERAND METHOD OF MAKING IT Application filed August 31, 1921, Serial No.497,113. Renewed .Tune 18, 1931.

This invention primarily relates to electrical condensers and method ofmaking them. The invention, however, is of general application and canbe embodied in condensers of the insulation are at a minimum.

Another object of the invention is to so construct the stack orcondenser elements that, when assembled within its casing, clamped andembedded, it will have and I maintain the desired capacity.

Another object of the invention 'is to provide an improved lead andterminal.

The invention consists of the features described in detail hereinafterand illustrated in the accompanying drawings, in which Figure 1 is asectional elevation of the Figs. 3 to 5 are sectional views of modifiedforms of insulators.

In high potential condensers now in use, especially in condensers usedinradio transmitters, it is common practice to provide a metal casingwhich constitutes the low potenti al terminal of the condenser, the highpoten tial terminal of the condenser extending through a suitableinsulating cover on the casing.

In the embodiment of the invention herein illustrated, Figs, 1 and 2, Ihave provided such a casing 1, preferably of metal having a removablebottom or closure 2 which is Secured in place on the casingcproper bymeans of screws 3 or solder, a suitable gasket 4 being interposedbetween the lower edge of the casing and closure 2. The closure 2, if sodesired, may be flexible to yield upon expansion of the filler W ofinsulating material 'exertedupon the stack, forcing is, the sheetscomposing the stack are arranged vertically at right angles to thebottom 2, and are maintained under pressure within the casing asfollows. A plate 5 is placed against one of the vertical sides of thecasing 1, this plate being machined andsmoothed and adapted to engageone end of the condenser stack S, thereby obviating the necessity formachining and smoothing off the interior of the casing 1, which is pref--erably cast, and may comprise aluminum or any suitable alloy of it orany other suitable metallic material. The stack S is maintained underpressure by means of a pressure plate 16 arranged at the opposite endofthe stack and engaged by ascrew 7 threaded.

through the opposite wall of the casing. By I adjusting screw 7 anydesired pressure, of

the order of thousands of pounds, may be plate 5, the pressure plates 5an 6 covering it against substantially the active area of the stack.

The pressure upon stack S is of an order to maintain the sheets of'foiland dielectric in intimate contact free from air and voids and I asnearly devoid as possible of insulating material such. as paraflin. Theorder of magnitude of the pressure exerted in an example of a commercialform of the condenser was bottomof the casin are flanges 8 constitutingsecuring flanges w ereb the condenser. may be mounted in any suita 1erack.

In the embodiment of the invention herein disclosed, the stack Scomprises a number of sections 9 having their foil terminals connectedin series alternately at opposite ends 10 by means of solder; Betweenthe sections are located separators 11 preferably of mica.

The terminals of the outermost sections or the sections at opposite endsof the stack have soldered to them copper stri s or leads 12 which arebent around the en s of stack approximately 2,200 pounds over the endsof the stack. Intermediate the top and the S and clamped between theplates 5 and 6 respectivelyand the stack S, being electrically connectedtogether through casing 1. In other words, the opposite ends of thestack S are at the same potential, being electrically connected to thecasing which constitutes the low potential terminal of the condenser.

In the embodiment of the invention herein disclosed, a high potentiallead 13 is secured to one of the foil connections 10 at the centralupper portion 14 of the stack whereby the stack S is connected in seriesparallel; that is, the two parts of the stack, one at each side of thelead 13, are connected in parallel,

the individual parts comprising sections con-- nected in series. Lead 13is universally flexible and is a stranded wire, preferably copper; thatis, a wire which is made up of a number of strands of very fine wire.The inner end of the lead 13 is flared or fanned out as shown (Fig. 2)with the individual strands soldered at spaced points along the foilconnection 14, whereby a very strong connection is secured between thelead 13 and the stack S. The fanned-out lead soldered to the foilterminal is disclosed in my co-pending application Serial No. 465,137,filed April 26, 1921, Patent No. 1,558,043, issued October 20, 1925,this present application constituting a continuation in part of saidco-pending application as to this feature. In constructions heretoforeused, it has been found that copper strips or similar connections whenconnected to the foil leads, which are very fragile, tend to becomedisconnected or torn therefrom and also tend to tear the foil terminals.By the present invention, this difficulty is obviated and strongpermanent means is provided for connecting the high potential lead tothe stack.

Inasmuch as the high potential lead 13 must be thoroughly insulated fromthe casing 1, which 'is the low potential terminal, and in order tomount lead 13 permanently upon the casing but insulated therefrom, Iprovide a rigid terminal such as a metal tube 15 through which the lead13 is threaded, as illustrated, the terminal 15 being located on thecasing at a point remote from closure 2. The metal tube 15 projectsthrough asuitable opening 1a in the casing 1, and is thoroughlyinsulated from the casing by means of an insulating device 16. In thepresent embodiment, this insulating device comprises a disc or plate 17,of insulating material, which is of an area greater than the area of theopening 1a within the casing and extending over the boundaries of saidopening. This disc is preferably of some material having high insulatingqualities and low loss such as mica, and should be so designed as towithstand the difference in potential betweenthecasinglandthe fiexiblelead 13 or the tube 15 throughwhich it passes. It is preferred that thisplate 17 consist of mica, which is one of the best materials for thispurpose,this plate 17 being clamped inwardly of its edge to the casing 1by means of a metal ring 18 and screws 19 passing through the ring 18into the casing 1, a suitable lead or rubber gasket 20 being interposedbetween the mica sheet andthe casinglto secure atight joint. The tubularmember 1 5 extends through the disc 17. Mounted around tubular member 15below the plate 17 is a lower insulating bushing 21 of reduced diametercompared to plate 17 and engaging the bottom of disc 17 and surroundingtube 15. This bushing is provided with one or more corrugations orgrooves 22 arranged circumferentially therearound to increase thecreepage distance and consists preferably of a laminated structure;

for instance a plurality of mica pieces or discs of diameter reducedcompared with the disc 17 and compressed together in the mannerhereinafter described. Mounted around the tubular member 15 below thebushing 21 is a second or bottom insulating bushing 23, likewise ofreduced diameter compared to plate 17 and preferably of some hardinsulating material which can be easily molded and machine-d such asphenolic condensation products and the like. The lower side of member 23is provided with concentric grooves or corrugations 24, whereby thecreepage distance between the lead 13 and tube 15'and the condensercasing 1 is increased, and with a central recess 25 between grooves 24adapted to receive a round nut 26 which is threaded and sweated on thelower end of the member 15. The bottom bushing 23 is provided instead ofmica because its flat surface, unlike mica, may be easil machined toform grooves 24 and recess 2 the bushing 23 insulating the lower end oftube 15 and nut 26. Upon the opposite side of the large mica plate 17 isan upper insulating bushing 27 of reduced diameter compared with disc 17mounted thereon and surrounding and -insulating the upper portions ofthe member 15. Like the bushing 21, the bushing 27 is also of laminatedinsulating material preferably built up of superimposed pieces or discsof mica and of decreasing diameter upwardly as illustrated, forming anupwardly tapering bushing.

The device 16 is preferably constructed or assembled on member 15 byassembling thereon bottom bushing 23 and the mica discs, plates orwashers in their proper order from bottom to top. In the embodimentherein illustrated, nut 26 is threaded on member 15 and bottom bushing23 is placed in position, v

member 15 to hold the mica sheets and pieces in position againstdislocation. The assembly of device 16 is then treated in a bath of hotmolten insulating material, which will act more or less as an adhesive,for about fifteen minutes until bubbles cease, either with or withoutthe application of vacuum. Suitable materials for this purpose areparaffin or sulfur. The assembly while hot and impregnated with molteninsulating material is compressed or clamped tightly by nut 29 andallowed to cool, thus clamping the mica sheets together in a solid massheld together by nut 29 (which may be pinned to member 15) and by thefusible insulation which has now solidified. The upper bushing 27 isthen cut, turned or ground to proper shape and polished, providing asmooth tapered surface 30. The bushings 21, 23 and 27 are thus retainedand supported on p1ate17 and held under compression entirely by means ofmember 15 and nuts 26 and 29. The groove 22 in lower bushing 21 isprovided by assembling intermediate mica washers of reduced diameter.

Above nut 29, in close contact with the nut and member 15, is aconcave-convex metal member 31, having its concave side 32 facing theupper bushing 27 and having its edge 33.

in vertical alinement with and spaced from the clamping ring 18. Theinclination of the surface 30 of the'bushing 27 and the curvature andspacin of the member 31 are so arranged with re erence to eachother andso proportioned that any difference of potential between the-oppositeends of the member 15 produces electrical stresses not through the upperinsulator 27 but mainly through the air from member 31 to the casing 1,main-' taining the electrical field parallel with the bushing 27 insteadof cutting the same. In other words, member 31 with casing 1 provides astatic shield preventing losses in the insulator 16'and the destructionthereof. The member 31 also performs additional functions in that itprovides a large-surfaced terminal for radiating heat generated in. the

stack and conducted through the lead 13 to member 31. The member 31 alsoserves as a protector or dust-guard for the insulating device 16,preventing deterioration thereof; that is, it is located above theinsulating disc 17 and the bushing 27. The corona member 31 is securedin place by means of a nut 34 threaded upon the upper portion of thetubular member 15,'and above this are located washer 35 and nut 36whereby any suitable lead may be attached to the high potential terminalin the usual manner.

I have also provided a novel spark-gap for association with thecondenser-to preventthe formation of excessive differences of potentialbetween the high and low potential portions thereof. For this purpose,the metal member 31 is struck down, forming a vertical part 37, on whichis mounted a roundended spark-pin 38 having a longitudinal Patent No.1,652,212, issued December 13,

1927. The process therein described covers the manufacture of a stack bypreliminarily dipping the individual sheets ofmica in suitableinsulating material, such as parafiin, and building what is called thematerial stack consisting of alternate sheets of foil and dielectric,and then treating the material stack thus formed in molten insulatingmaterial a such as parafiin and applying high compression and cooling,forming a solid block; After this, the material stack is split up intosections, such as the sections 9. The projecting foil terminals areconnected as at 10, and,

the insulating separators 11 inserted. Of course, the sections may beassembled and connected by any desired method. For instance, eachsection maybe built up under wax, heated, compressed and cooled underpressure. Each section is then tested for capacity and voltage.The-sections are then connected in series and separators insertedbetween them. After the sections have been connected by solder and thesectional separators 11 positioned, the high potential flex. ible lead13 is soldered in afanned-ont manner to the intermediate connection 10,and the two low potential leads 12 are soldered to the free ends of theend sections. The

stack is then placed on the base of a buihl ing stand provided with fourvertical rods having vertical notches upon their innersides adaptedtoreceive the corners of the condensers stack; or, if so desired, a standhaving six rods may be used, two rods engaging each' side of the stackand one at each end. 'A stand adaptable for this purpose is disclosed ina pending application of Pickard Serial No. 380,919, filed May 12, 1920,Patent No.

1,706,816, issued March 26, 1929. The stack when positioned in the standis supported and braced by the'vertical rods against dislocation andside slip. The stack andstand are then placed in a hot moltenparaflinbath for approximatelytwenty minutes until the stack is warm, the bathbeing at approximately a temperature of 150- C., or in a bath of anysuitable insulating material. The stack and stand are then removed fromthe bath, and the stack while still in the stand and while still hot isplaced under a pressure slip while underthe great pressure- The of theorder of magnitude of a ton per square inch over the active surface ofthe stack, and allowed to cool under pressure before being "placed inthe final condenser structure of easing 1,'the vertical rods of thestand supporting and bracing the stack against side stack while underthe pressure of the order of magnitude above-mentioned and after coolingis tested for capacity, and the capacity finally adjusted to its correctvalue, if this is necessary. Thus it will be seen that the final andcorrect capacity can be obtained before the stack is finally clamped inthe casing 1 and embedded, thereby avoiding the removal of the fillerafter finally embedding for the purpose of obtaining desired capacity,if on test the capacity is found to be wrong. By cooling the stack underpressure outside of the casingl in the manner abovedescribed, the stackcan also be tested for breakdown and phase angle before being placed inthe casing 1 as well as measured for final length. Furthermore, by thuswaxing and cooling the complete condenser stack,

including the separators 11, before being placed in casing 1, it can behandled as a block and side slip cannot occur during the fillingoperation afterthe stack S is placed Within the casing 1 and maintainedunder pressure by members 5 and 6. 7

In former processes and methods of bullding stacks and assembling themwithin the condenser casing, wax treating, compression and coolingoperations on the completed stack, (including the separators 11 inplace, as well as the final adjustment of capacity) usually were donewith the s ack in a permanent clamp forming part of the condenser and inthe condenser casing. In that process, however, it was dilficult tomaintain good stacks where the length of the base exceeded by over twicethe largest dimension of the stack or where sectional separators hadbeen inserted. Such length of stack by reason of the greater number ofsections and the greater number of sectional separators tended to causethe side slip above referred to, upon final compression, that is, wherethe stack was relatively high or had separators which ;had notpreviously been waxed, or both, upon "compression, the elements of thestack tended to be displaced relatively to each other. By

providing lateral support for the stack dur ing compression, thisdifliculty is obviated.

After the. stack S, including the separa-.

tors 11, has been waxed and compressed,

cooled and tested as above described, it'is in condition to be handled,being cold and covered with wax and is directly secured within thecasing 1 by means of the clamping members 5 and 6 and adjusting screw 7.The terminal gasket 20 is then positioned and the flexiblelead 13 pulledup through the vertical hole through the member 15. The insulator 16,including the disc 17, is then clamped to the casing 1 by means of ring18 and screws 19. The lead 13 is then pulled up taut through member 15and its excess length cut 0E. The outer end of lead 13 is then solderedto the top of member 15, which is provided at its upper end with arecess or countersunk portion 41 (Fig. 1) which fills with solder,retaining lead-13 in place and electrically connecting it to member 15.The bell 31 and remaining nuts are then assembled and spark-pin 38properly located. This method of connecting the flexible lead from thestack S to a rigid metallic terminal is novel, inasmuch as in thepresent instance the soldering of this lead to the terminal is at apoint outside of the casing where it is accessible and where thesoldered joint can be end 41. Furthermore, inasmuch as I have utilizedin the present invention the stranded wire 13, the strands at theirouter ends provide additional means for securing a very good electricaland mechanical connection with the terminal 15. After the parts havebeen assembled as illustrated in the drawings, with stack S held bymembers 5 and 6 under sufficient pressure to hold it in place, the wholecondenser can be inverted, the bottom 2 being removed, and the sameembedded in the manner described "in my Patent 1,652,212 above-mentionedto provide a compact, nonporous, holosteric embedment W for the stackand around lead 13 and terminal 15 withinthe condenser 1, which is freefrom air and voids. As described in such Patent 1,652,212, a head orextension issecured to the casing and thecasing and extension arepreliminarily heated by filling the same with molten paraflin at atemperature around 140 0. While thus filled, the final pressure isapplied to stack S by tightening up screw 7. The

molten parafiin is then-removed and vacuum applied and the head andextension filled with molten paraffin or other insulating filler whichis allowed to solidify in the manner describedin said Patent 1,652,212.The diameter of the passage through member15 should be such as to allowlead 13 to be pulled through while the solder at 41 makes a tight joint.In some cases, the preliminary heating with parafiin may be omitted'andthe stack S finally clamped under high pressure as soon as of by meansof positioned. The condenser stack and terminal lead 13 are then embdded and the head and surplus wax or insulating material removed asdescribed in said Patent 1,652,212. After the embedment, the bottom 2,with its intervening gasket 1, is secured in place by means of thescrews 3, the closure 2 being flexible, to allow the expansion of thewax, if rcqnired.

The soldering of the fanned-out stranded wire end to the foil terminalis a distinct advantage in cases of condensers'having sections of lowcapacity; that is, having a small number of foils in a tab, because thefewer foils you have the more easily the foils are torn. The connectionof the lead 13 to the stud 15 at the upper end thereof is made after thestack and terminal are in place in the easing, and places the solderedjoint outside the casing where it can be properly made and in spected.Before the top joint is soldered, however, the lead 13 should be pulledup tight with the hand.

The insulator 16 provided for the high potential terminal of thecondenser, for the purpose of insulating such high potential terminalfrom the casing, provides a long creepagc path with short height. Thisincreased creepage path is obtained by means of the ottom insulatingbushing 23\turned with two concentric grooves 24 and machined at thecenter 25 to contain the lower end 26 of the high tension stud 15whereby it is secured on the stud. Furthermore, additional creepage isobtained by providing circumferential grooves in either or both of theupper and lower micabushings 27 and 21 upon either or both sides of themica disc 17. I have shown one such groove 22 in the mica bushing 21below the disc 17. In'the present construction, the insulator 16comprises a single mica disc 17 clamped to the casing 1, and built-updiscs of mica of reduced diameter forming bushings 27 and 21 upon andsupported by the disc 17, the bushings being clamped to the disc 17 atopposite sides therethe member 15 and co-operating nuts threadedthereon. The drawings show how, in order to permit a narrowcasingopening, with electrical and mechanical safety, the casing andstatic shield (or corona shield as it has become known in the art),

are curved or inclined with relation to one another and to the stack, sothat, allowing for the necessary distance between casingparts 1 and 18from terminal lead 15, the casing is safely remote from the portions ofthe stack of the higher capacities, and even so, any

break-down which may occur will involve av discharge from corona shieldto casing in shunt to the insulating material and the itself, (withorwithout the spark-gap elec-, trode according to the desired design).The narrow casing-opening is important because it is bridged byinsulating material always stack 4 structurally weaker than metal. Theinvention in these respects is an improvement upon condensers of thetype shown in patent to Dubilier 1,229,914 of 12 June 1917 where thecover which insulated the high potential lead from the metal casing wasrequired in practice to be not only large in superficial area but verythick, in order to withstand the stress of a stack grown hot in serviceand tending to expand against the insulating cover which was one of theclamping members. In the present invention, not only is the insulatingcover relieved of all functions of holding the stack under compression,but the casing-opening and therefore the insulating cover are so narrowas greatly to contribute to the practicability of the combination including the insulating cover. In the form shown, as usually in practice,the insulating cover is so narrow that it will not permit passage thruit of the stack in making the assembly, both the stack and the moltenwax being inserted thru the bottom casing-opening which is made largefor the purpose of readily permitting insertion of the complete stack asa whole inside the casing.

In Figs. 3-, 4 and 5, I have illustrated slightly-modified forms ofinsulating devices 16 for use such as in condensers for insulating highpotential terminals. In Fig. 3 is illustrated the large-diametered micasupporting sheet 17 clamped in the manner above described and having onopposite sides thereof the lower and upper bushings 21 and 27 as abovedescribed, of reduced diameter. In this form, however, the terminalmember 15 by which the bushings 21 and 27 and disc 17 are clampedtogether has an integral head 15a at one end, and as here illustrated,at the outer end, and a nut 150at the opposite end which, upon beingtightened, clamps the two bushings 21 and 27 and the insulating disc 17together between the nut 150 and head 15a. The insulator illustrated inFig. 3 is assembled substantially like that above described, but in thereverse manner; that is, from top to bottom the mica washers or piecesconstituting the upper bushing 27 are first assembled upon head 15a andfinally the mica washers or pieces constituting the bushing 21. The nut150 is then positioned and tightened up, the whole being treated andimpregnated as above described. In the con struction of Fig.3, insteadof utilizing nuts threaded upon the member 15 for the purpose ofsecuring an external lead, I have provided a vertically-arranged member15?) to which the lead may be secured, this member 156 being at rig tangles to and integral with part 15a.

In the form of the invention illustrated in Fig. 3, the bakelite dilectobushing 23illustrated in Figs. 1 and 2 is omitted, and in lieu thereof Ihave shown the bushing 27 corrugated at 27a whereby the creepagedistance is increased without materially increasing the length of theinsulator. The lead 13 is secured to the terminal 15 of Fig. 3 in themanner described in connection with Figs. 1 and 2.

Referring to Fig. 1, the construction shown therein differs from theconstruction of Figs. 1 and 2 in the omission of the bushing 23 composedof a phenolic condensation product or other suitable plastic, and inlieu thereof the upper bushing 27 is corrugated at 27 a. In otherrespects, the assembly is like that of Figs. 1 and 2, the nut 150corresponding to the nut 26 of Figs. 1 and 2, directly engaging thelower bushing 21 instead of the bakelite dilecto bushing 23.

In Fig. 5, I have illustrated another form of the insulator 16 whichcomprises the main or large mica supporting sheet 17, which may be ofany desirable configuration and secured as above described, and havingon opposite sides thereof the lower and upper bushings 21 and 27 ofreduced diameter and comprising laminated structures made up of sheetsor pieces of mica above described. The construction of Fig. .5 differsfrom that of Figs. 1 and 2, however, in the provision of a high tensionterminal 15 which may comprise a solid bolt upon which are threaded themica discs, washers or pieces comprising the lower bushing 21, sheet 17and the upper bushing 27. The inner end of the bolt or terminal 15 isprovided with an integral head 15m having a transverse slot 15% therein,to which in the slot 150% the lead 18 is soldered. The partsare'assembled, as above described, upon the head 15m, and thereafter thenut 29 is tightened, holding the several discs or mica washers inposition upon bolt 15, tightly between head 15m and nut 29, the

. parts being treated with wax as above described. It should be noticedthat the construction of Fig. 5 difiers from the construction of Figs. 1and 2 in the provision of a solid terminal 15 to which the lead 13 isattached at the inner end thereof instead of being threaded through theterminal 15 and soldered to the outside or outer end.

It is to be understood that the invention is not limited to theembodiments and fea tures specifically shown and described herein, butthat such embodiments and features are subject to changes andmodifications without any departure from the spirit of the invention.

I claim 1. In an electrical condenser, a metal casing having openings atopposite ends, a member of insulating material closing one of saidopenings, a terminal lead extending through I said insulating member,said insulating member surrounding a portion of said lead which projectsoutside the casing, a stack clamped within the casing and havingelectrical coni nections with the casing and stud respectively, a fillerof insulating material filling the casing and engaging said insulatingmember, and placed within the casing through the opening remote fromsaid terminal lead, and. a closure for said remote opening.

2. In an electrical condenser of the metal foil type comprising a metalcasing enclosing condenser elements and having an opening for a terminaltherefrom which is insulated from the casing, the improvement whichcomprises a tubular metal stud projecting through the casing; and astranded conducting, lead having one end extending through said stud andelectrically cormected to a part of the stud which is accessible fromthe out side of such casing, the other end of said lead having itsstrands separated from one another and conductively connected with a setof mutually connected foils at points located successively along theedge of the set of foils, to provide a strong connection relatively tothe fragility of the foils.

3. In an electrical condenser of the metal foil type comprising a metalcasing enclosing the condenser elements and having an opening for aterminal therefrom which is insu lated from the casing, and having aninsulating embedment in the casing around the condenser elements andterminal, the improvement which: comprises a tubular terminal studprojecting through the casing; and a stranded conducting lead having oneend extending through said stud and electrically connected to a partthereof which is accessible from the outside of such casing; the leadextending through said insulating embedment to'the condenser elements,said end of the lead havin its strands .separated from one another andconductively connected with a set of mutually connected foils at pointslocated successively along-the edge of the set of foils, to provide astrong connection relatively to the fragility of the foils.

{1 In an electrical condenser comprising a. metal stack enclosingcondenser elements and having an opening for a terminal therefrom, theimprovement in supportingthe terminal independently of the condenserelements and insulating it from the casing, which comprises acentrally-perforated sheet of .mica mounted on the casing over itsopening; an insulating material fluid when heated but solid at ordinarytemperatures and compacted against the inner surface of said mica sheet;a metal annulus outside the casing arranged to secure the mica sheetthereto; a terminal stud' projecting through the central perforation inthe mica sheet and extending on both sides thereof in and out of thecasing and having electrically connected to its, inwardly projectingportion a flexible lead connected to the condenser elements within thecasing, and a plurality of centrally-perforate'd mica sheets laterallysurrounding said stud and lying adjacent thereto and v1 to said micasheet, said stud projecting beyond said plurality of mica sheets.

5. In an electrical condenser comprising a metal casing enclosing thecondenser elements and having an opening for a terminal therefrom whichprojects through said opening and is insulated from such metal casing,the improvement which comprises an insulating member supported by thecasing and proecting eaterlorly thereof and surrounding such terminal,and a metal bellshapcd member mounted on said terminal and having itsconcavity facing and extending around said insulating member and towardsthe metal casing-and electrically spaced from the latter, saidinsulating member extending into the concavity of the metal bell havingan exterior configuration generally corresponding with the configurationof the concavity of said bell and the exterior projecting portion ofsaid bell and insulating member having relative configurations which aidin divertmg electrical stresses from the insulating member.

6. In an electrical condenser comprising a metal casing enclosing thecondenser elements and having an opening for a terminal lead from suchelements which extends through said opening and. is insulated from suchcasing, the improvement which comprises a metal bell-shaped membersupported by such terminal lead outside such casing and arranged withits concavity toward the easing opening, said bell member being in goodcontact electrically and thermally with such terminal and having adiameter of the order of'that of the opening in such metal casing; saidbell member being arranged to have atleast a portion of its rim closerto the casing than the distance between the rim of the easing openingand said terminal.

7 In an electrical condenser comprising a metal casing enclosing thecondenser elements, electricallyconnected thereto to constitute aterminal thereof, and having an opening for another terminal thereofwhich extends through such open ng and is insulated from such casing,the improvement which comprises a metal shield mounted on] such terminaloutside the casing and over the casing opening, the same being in goodcontact electrically and thermally with such terminal; and a spark-gapedectrode mounted on said metal shield and spaced from the metal of thecasing to constitute a spark-gap between the metal shield and metalcasing,

said electrode being located closer to the metal of the casing than issaid second ter minal. a v

8; In an electrical condenser comprising a metal casing enclosing thecondenser elements, electrically connected thereto to constitute aterminal thereof, and having an opening for another terminal thereofwhich extends through such opening and is insulated from such casing,the improvement which comprises a metal shield mounted on andelectrically connected with said second terminal in position outsidesaid casing and over the casing opening; and a metal member spaced fromthe metal of the casing and constituting an electrode to establish aspark-gap between said shield and easing, said electrode having asupporting connection with said shield for movement of the electrode toand from the casing independently of any such movements of said shield.

9. In a high potential capacitor of the type wherein the condenseritself is enclosed by a metal casing connected to the condenser as aterminal thereof and having an opening for the outward projection ofanother terminal of the enclosed condenser, the combination with suchother terminal projecting a substantial distance outside of the casingbeyond the metal of the casing around the casingopening; of aninsulating member closing said opening and extending around the sides ofthe projecting terminal beyond the metal of the casing around theopening; and a metal member located between the metal of the casingaround the opening and a portion of the projecting terminal extendingbeyond the insulatingmember, said metal member extending around theprojecting terminal and insulating member and being inclined asubstantial length of the insulating memberaround the projectingterminal away from the casing.

10. In a high potential capacitor of the type wherein the condenseritself is enclosed by and electrically connected to a metal casinghaving an opening and a terminal-lead from the enclosed condenserprojecting out thru said'op'ening, the improvement which comprises, incombination with a member consisting of insulating material, perforatedfor roje'ction of the terminal lead, and located between the projectingterminal and the metal ,casing, of a substantially bellshaped memberconsisting of metal extending curvilinearly intermediate a portion ofthe terminal-lead lying beyond said insulating member, and the metal ofthe casing around said lead-opening, the rim of said bell extendingcloser than the projecting terminal lead to the metal of the casing andthe bell terminal lead projecting from a high potential portion of thecondenser out thru said opening to a substantial distancefrom the metalof the casing; the sides of the casing at their tops being inclinedupwardly and inwardly to end at said casing opening-at a safe distancefrom the high potential portions of the enclosed condenser, saidinclination providing a casing-opening of short diameter; an insulatingmember of correspondingly short diameter closing such casingopeningand-projecting substantially beyond the casing and around a substantiallength of the projecting portion of said terminal lead; and a coronashield extending from a position near'the metal rim of theshort-diametered casing opening to a portion of the projecting terminallead beyond the projecting portion to said insulating member, saidshield in such arrangement having a diameter correspond ing with that ofthe casing-opening and insulating member and being inclined from theprojecting terminal and toward the metal of the casing.

12. A high potential condenser in a metal casing formed with openings inopposite Walls, a terminal lead projecting out thru one of said openingsfrom the condenser to a substantial distance from the'metal of thecasing; the ends of the casingwalls near said terminal lead openingbeing inclined thereto to end at such opening at a safe distance fromthe high potential portions of the condenser and provide an opening toosmall for insertion of the condenser into the casing; an insulatingmember of small size corresponding to and closing saidsuch smallcasing-opening and a corona shield for said insulating member, saidshield being ofsmall diameter corresponding with that of said smallercasingopening and insulating member and inclined toward the casing-wallof said opening from electrical connection with a portion of theprojecting terminal lead which is remote from the metal of the casingsaid opposite ,casingopening being sufficiently large for insertion ofthe condenser in the casing.

13. In a high potential condenser, the combination with aseries-sectional stack, of a metal casing therefor connected with aterminal thereof and formed with an opening, a terminal-lead projectingfrom a portion of the stack at high potential difference from the casingand out thru said opening to a suitable distance from the metal of thecasing; an insulating member closing said opening and projecting outsidethe casing and extendmg around the projecting portion of theterminal-lead outside the casing; and a metal static shield extendingaround the sides of the projection portion of said insulating memberelectrically connected with a portion of said projecting terminal lead,and formlng an electrode of an air-gap between itself and the metal ofthe casing, said gap being shorter than the distance between the metalof the casing and the portion of the shield to which said terminal-leadis connected.

14. The improvement on the type of high potential condenser wherein thestack was clamped in a metal casing by a cover of insulating materialand wherein the stack was connected to the casing as one terminal andthe other such terminal .was a lead extending out centrally thru suchinsulating clamping cover, said improvement consisting in causing thestack to be clamped between the sides of the metal casing itself therebyreducing the necessary thickness of the insulatingcover necessary as amechanical clamping element; and further, in combination, causing thesides of the metal casing to' be inclined toward the central projectingterminallead without unduly approaching an end or the portion of thestack'to which said lead is connected thereby reducing the width of thecasing opening for said lead and reducing the superficial diameter ofthe insulating cover necessary when the casing sides are straight orinclined away from the central projecting terminal-lead.

15. The combination with a high potential condenser stack, of anenclosing casing of metal therefor connected with a terminal of saidstack and having an opening opposite an intermediate portion of saidstack, a second terminal of said stack projecting outside the casingthru said opening, an insulating member closing said opening and alsoprojecting outwardly beyond said opening around the projecting portionof said terminal; and a bell-shaped member of metal located beyond saidprojecting portion of said insulating member, concave to the casing andextending conductively from a portion of said projecting terminal beyondthe projecting portion of said insulating member to a position in spacewhich is closer than said terminal to the metal of the casing; thebellshaped member being arranged for enclosing a correspondingly greaterlength of the insulating member around the projecting portion of theterminal, and constituting the more a mechanical protection for thematerial of the insulating member.

16. A high potential capacitor comprising a stack of capacitor elements,a metal casing enclosing and holding said stack under pressure andprovided with an opening on one side through which said stack isinserted,

means for closing said opening, the opposite end of said casing beingprovided with a smaller opening smaller'than the stack dimensions, aterminal connection for said stack passing through the smaller opening,the opposite stack terminal being connected to the casing, an insulatingmember closing said smaller opening and extending around said terminalconnection beyond said casing,

the walls of said casing between said smaller opening: v and tile:adjacent "portion of V the stack sloping inwardly-toward I said smalleropening andyterminal connection and away I from saidstack: at. a safedistance and being flattened around said smaller opening, and a fusibleinsulating material filling the casing surrounding the stack andcontacting with said insulating closure for said smaller openmg. Y

1 17. A high, potential capacitorcomprising a metal casing, a stack ofcapacitor elements therein electrically connected at one end to saidcasing, the casing having anopening on one side of a size too small forinsertion of said stack therethrough, and the walls of said casingengaging and compressing the stack-ends and being strong enough towithstand the pressure on said stack, a terminal conductor connected tosaid stack and passing out of the casing through said small opening, aninsulating member closing said opening and projecting beyond said casingaround said terminal conductor, means for opening the casing forinsertion of said stack, a fusible insulating material surrounding saidstack and filling said casing, at least two opposite walls of the casingbeing provided with integral extensions which are arched about the stacktoward said small opening for supporting said terminal conductor, the

' spacing between said stack and at least a por tion of the archedextensions increasing with increase in the potential gradient betweenthestack elements and easing.

18. In an electrical condenser, a metallic casing-casting-formed withopposite openings, a condenser member therein located between saidopenings and the casing walls; an

insulating embedment-castin in the casing and around the encased conenser member; one of said openings being sufiiciently largeforintroduction of the condenser member therethru into thecasing; a leadconnected to the enclosed condenser 'member and extending'out from saidcasing thru the other opening;'and a cover of structural insulatingmaterial closin said other opening and extending arounf said leadinsulating it from the casing, and secured to the casing, whereby thecombinationof the casing, insulating cover-and said lead constitutes,when thecondenser member is in place inside the casing, a-mold for thefiller-casting between the easing and the condenser v member which it;encloses: L 1

i219; an electrical condenser, 1 a metallic casing=casting formed-withopposite openings; a condenserstack encased thereby and arrangedwith itsends' facing-opposite closed walls-ofxthe casing and its opposite sidesfacing said opposite openings; means clamping said? stack ends:betweensaid closed casing 'wallsfiand tending to ,force' said :wallsapart;-

one oi 'said o'pem being sufliciently large for introduction 0 saidcondenser member therethru into the casing; .alead connected tosaidenclosed stack and extending thru the relative to the length of theenclosed stacks and to the distance between the walls of the casing, anda cover of structural insulating material closing said small opening,extending between the casing and said lead and surrounding the outwardlyprojecting portion of the lead for a substantial distance beyond theexterior of the casing; said casing having an arched formation betweensaid small opening and the wider main casing portion and impartingsubstantial rigidity to the casing resisting the tendency of saidclamping means to force apart the closed casing walls between which thestack is compressed.

20. In an electrical condenser, a metallic casing-casting formed withopposite openings; a condenser member encased thereby and locatedbetween said openings and the casing walls; an insulatingembedment-casting in the casing and around the encased condenser member;one of said openings being sufficiently large for introduction of thecondenser member therethru into the casing; a lead connected to theencased condenser member and extending thru the other and oppositeopening to a substantial distance out? side of and beyond the metal ofthe casing; and a cover of structural insulating material closing saidother opening, secured to the casing and extending around said leadinsulating 1t from'the casin and extendlng a substantial distance beyonthe metal of the being sufliciently large for intro uction, of thecondenser member therethru into the. cas ing-;a lead connected totheeneas'ed condenser member and extending thru the other and oppositeopening to .a substantial. distance denser member; one of said casin-openings outside of and 'be yondfthe metal of the casing, saidleadbeing centrally with respect to the interioroi thecas'ing and saidlead-opening; and, a} cover of structural- "insulating material closing]said lead-opening se d. o th a in' idz s ir i g u said lead insulatingit from thec'a'sing and a side facing the-larger casing-opening; an

therein, the casing bein ing and the lead whereby the lead-opening isrelatively small; the metallic casing itself also having aform archedfrom its wider main portion to said smaller lead-opening and generallyconforming with the potential gradient of the condenser member andcentrally disposed lead.

22. In an electrical condenser, a metallic casing-casting formed withtop and bottom openings; a-condenser member encased thereby and locatedbetween said casing-openings and casing-walls; an insulatingembedmentcasting. in the casing and around the encased condenser memberand between it and the casing walls; said bottom casing-opening beingsufficiently large for introduction of the condenser member therethruinto the casing; a lead connected to the encased condenser member andextending thru the top opening to a substantial distance outside, of andbeyond the metal of the casing; and a cover of structural insulatingmaterial secured to the casing around said lead-opening closing the sameand surrounding the lead and extending a substantial distance beyond themetal of the casing providing a long creepage path between the casingand the lead whereby the lead-opening is smaller than theenclosedcondenser-member; the combination of the casing, the insulatingcover and the lead extending thru the cover constituting a closed moldfor the insulating embedment- 'casting between the casing and thecondensermember which it encloses.

23. In an electrical condenser, a box-like metallic casing, acondenser-member enclosed formed with an opening sufficiently large orthe introduction of the condenser member therethru into the casing; aninsulating embedment-casting inside the casing and aroundthe encasedcondenser-member; said casin being formed with a relatively small'lea-opening opposite said larger opening and smaller than the encased conenser member; a lead extending from the encased condenser member:and-out of the. casing thru said lead-opening; and an insulatorsurrounding said lead and closing said lead-opening;'said casing,insulator and lead constitutinga closed mold for the insulatingembedment-castin 24. In an electrical con enser, a box-like I metalliccasing formed with opposite large and small openings; a condenser-memberenclosed therein, and arranged with its ends insulatingembedment-casting in the casing- .and around the condenser member; alead said lead and insulator closing the wall of the casing in whichsaid smaller opening is formed; the larger casing-opening beingsufficiently large for the introduction of the condenser-membertherethru into the casing, and the assembly of the lead, lead-insulatorand casing with large opening constituting a closed mold for saidinsulating embedmentcasing and around the condenser-member; a

lead from the encasedcondenser member and extending out of the casingthru the smaller top lead-opening, said lead and insulator closing thetop of the casing; the larger bottomopening being sufliciently large forthe in troduction of the condenser member therethru into the casing, andthe assembly of the lead, top lead-insulator and easing with largebottom-opening constituting a closed mold for said insulatingembedment-casting;

26. In a high potential electrical condenser, a metallic casing-castingformed with opposite large and small openings, a seriessectional highpotential condenser stack encased thereby and arranged with its endsfacing opposite closed casing wallsand its sides facing said 0 positeopenings; means clamping said stac -ends between said closedcasing-walls and tending to force said walls apart; one of saidcasing-openings being sufiiciently large for the introduction of thecondenser-stack therethrn into the casing;

yond the metal thereof providing a longcreepage path between the latterand the projecting portion of the lead and providing for alead-openingsmaller than the condenserstack; said lead being disposed centrally ofthe lead-opening of the casing, and the easing having an archedformation between the lead-opening. and the main casing-portion a nd imarting substantial rigidity to the casing reslstingthe tendency of saidclamping means to force apart the closed casin -walls bet-w n which thestack is compresse said arche casing-portion generally conforming to thepotential gradient of the condenser stack and centrally disposed lead;and the assembly of metallic casing, insulating cover and said leadconstituting, when the con-.

denser stack is clamped in place inside the casing, a mold for saidinsulating embedment-casting. v

27. In a high potential condenser, a metallic casing-casting formed withopposite large and small openings, a condenser-member encased thereby,said larger casing-opening being sufficiently large for the introductionof the condenser member therethru into the casing; a lead extending fromthe condenser member thru the smaller casing-opening and extending asubstantial distance outside the casing beyond the metal thereof; a

and closing the lead-opening, constituting a closed mold for saidembedment-casting providing access for the latter to the interior surfaces of the insulating cover.

28. In an electrical condenser, a metallic casing-casting formed withopposite large and small openings, a condenser-member encased therebysaid larger casing-opening being sufficiently large for the introductionof the condenser-member therethru into the casing; a lead extending fromthe condenser member thru the smaller casing opening and extending asubstantial distance outside the casing beyond the metal thereof; acasingcover of structural insulating material secured to the casing,extendin around said lead and closing the lead-opening of the easing; aninsulating embedment-casting inside the casing covering the surfaces ofsaid insulating cover which face the interior of the casing therebyeliminating interior creepage surfaces along short distances between themetallic casing and the lead; the insulating cover extending asubstantial distance outside and beyond the casing around the projectinglead constituting a long exterior creepage path between the metalliccasing and the stituting a closed mold for said embedmentcastingproviding access of the embedding material thru the largercasing-opening to the interior surfaces of the insulatin cover.

WILLIAM H.'PRI SS.

lead; and a metallic static shield electrically connected and secured toa portion of the lead lying beyond the insulating cover and surroundingthe lead and desirably spaced from the metal of the casing; the assemblyof the lead, casing and insulating cover secured thereto and closing thelead-opening, con-

